The spatial and social organization of (1) freely growing and (2) regulated growth laboratory populations of house mice at different stages of crowding are being examined. In freely growing populations, the social structure consisting of small, spatially distinct groups collapsed as the density increased. The whole population merged into a single, homogeneously distributed group as the mice began to lose their individual sociospatial identity. In a population in which the growth rate in regulated, spatially distinct social groups are maintained for longer periods during each generation and at a higher population density than in freely growing populations.